sEMG: Surface Electromyography – Jeffrey R. Cram

Ask the Practitioner

Why should the Physical Medicine Practitioner be interested in sEMG?

Many physical medicine practitioners work with soft tissue problems. While traditional methods of assessing pain related problems, such as radiographic techniques, needle EMG studies and Nerve Conduction Velocity studies are well suitable for bone and nerve related problems, they are insensitive to muscle, tendon, ligament and articular dysfunctions. And traditional methods for assessing soft tissue pain related problems, such as palpation, are ultimately subjective.

Surface EMG technology specifically monitors muscle action potentials (MAPs), and this is known to be sensitive to soft tissue injuries. For example, in some cases of dysfunction among homologous muscle pairs (or between agonist and its antagonist or synergist) there is an imbalance in relative stiffness in the muscles that participate in a specific movement. Such imbalances are thought to be due to faulty central nervous system motor control problems, along with peripheral factors such as inefficient length-tension relationships and passive myofascial compliance. When the practitioner puts the sEMG findings together with clinical examination (from evidence of, segmental and supra segmental motor reflexes, sympathetically mediated reflexes, instabilities, articular and periarticular factors, nutritional factors, beliefs, attitudes and affect of the patient), the relationship between muscle impairment and other physical and psychologic factors becomes clearer.

Correct classification of impairment with observed functional limitations may be used to derive treatment planning in a thoughtful way. Surface EMG techniques and associated feedback displays can make treating the patient more efficient. For example, sEMG can help identify inappropriate muscle substitution patterns and thus refine therapeutic exercise prescription. Motor copy templates can be used to assist in learning new recruitment patterns. And sEMG triggered electrical stimulation is has been shown in some studies to facilitate the rehabilitation process.

Lastly, sEMG monitoring provides objective documentation trail of the impact of the physical therapy on muscle function, thus allowing the therapist to demonstrate gains both to the patient and third party payer.

Can sEMG be useful in Therapeutic Exercise prescription?

In physical medicine, it is extremely important that the patient practice stretching and strengthening exercises on a periodic basis. Today, it is very common to teach a patient a set of exercises and give them a handout to remind them of what they are to do until the next visit.

What sEMG monitoring of an exercise prescription does is guarantee that the exercises are activating the desired and targeted muscle group(s). sEMG monitoring better assesses the patient’s actual ability to activate the desired muscle, without muscle substitutions or co-contractions. If necessary, the therapist can refine the home exercise instructions for the patient to make it more effective.

Does sEMG monitoring have a role to play in postural assessment or training?

Posture is an important part of physical medicine. If the posture is bad, movement may be compromised or muscle substitutions may appear.

sEMG monitoring allows the therapist to better quantify the muscular efforts dictated by posture. A head forward position in a patient with cervical pain will, in all probability, show elevations in the cervical paraspinal muscle activity. If this is the case, one could argue that the cervical pain is potentially maintained either by the weight of the head placing an undue strain on the peri-articular structures or by the build up of lactic acid associated with muscular efforts required by the posture.

While the therapist can instruct the patient in how to move their head back into better postural alignment, it is much better to show the patient how the muscles at the back of the head can relax with a postural correction. Many a patient of mine has finally caught onto the necessity of postural correction based upon what the sEMG has taught them.

Can stretching be assisted by sEMG monitoring?

Stretching is more effective if the muscle relaxes during the stretch. The problem is that when muscle tissue is stretched, the stretch receptor gets stimulated causing the muscle to become active.

sEMG monitoring during stretching can be used to assist the patient in relaxing the muscle during the stretch . This is because the muscle spindle is, in part, under voluntary control. By learning to breathe into the stretch and to relax into the stretch, the soft tissue has a better chance of actually elongating. The sEMG signal can be used to guide the patient quieting the muscle being stretched. This could accelerate the rehabilitation process.

Cram JR and Bittman B. Surface Electromyography: An Electrophysiological Alternative in Pain Management. In Weiner R (ed), Pain Management: A Practical Guide For Clinicians, St Lucie Press, Boca Raton, Fl, 81-96, 1998.

Kasman G, Cram JR, Wolf, S and Barton, L. Clinical Applications in Surface EMG: Aspen Publications, 1997.

Jetti AM. Physical disablement concepts for physical therapy research and practice. Physical Therapy, 1994, 74:380-386.

Cram J.R. Clinical EMG For Surface Recordings (Volume 2). Clinical Resources, Nevada City, CA 1990.

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